Good point about the cats! I forgot to mention that we found him om nom noming on some kitty poo as if they were cookies, so we have designated one room the Kitty sanctuary and barred it with a baby gate. That room is where they get fed and where their litter trays are kept.
At the moment, the dynamic seems to be that the cats are happy to ignore him if he's sitting calmly somewhere, while his calmness starts to wane as soon as he spots a furry friend to play with. We're working on discouraging the signs leading up to a dash (deep voiced and firm NO to distract him from staring at the cats) and praising him if he spots a cat and does not try to run to them, so I am hoping they will settle in *eventually*.